We are remodeling our pool deck and want to hang sun sail. The measurements for the area we are covering are 17X17. My questions are:

1.) Should I buy a slightly larger (20X20) or smaller 16X16 sail? And then would I do posts at the exact distance apart for the size of sail (16 or 20 feet)?

2.) Any advice on how to determine height of the sail? Should I do at different heights for each of the 4 postings??